Photographic elements often contain filter dyes for a variety of purposes. Filter dyes may be used as absorber dyes in photographic emulsion layers to improve image sharpness or adjust photographic speed. They may be used as antihalation dyes, for example, in a lower layer of an element to reduce halation in the image-forming layers. Filter dyes can also be used as general purpose filter dyes for absorbing light of a particular wavelength so that it does not expose or exposes at a reduced intensity a lower layer in the element.
Filter dyes may be present in essentially any layer of a photographic element where it is desired to absorb radiation in the region of the spectrum where the dye absorbs. For example, they may be contained in an interlayer, a radiation-sensitive layer, an overcoat layer, an undercoat layer, a backing layer, or others known in the art. Absorber dyes (also called integrain absorber dyes) are generally present in the radiation-sensitive layers of photographic elements. Antihalation dyes may be located in undercoat layers on either side of a transparent support carrying radiation-sensitive layers. Such antihalation layers may also be positioned between two or more radiation-sensitive layers in a multilayer element or as a backing layer on the side of the support away from the light-sensitive layer.
Photographic elements are often used in conjunction with information-recording equipment that exposes the element with infrared radiation emitted from a semiconductor laser diode. For example, in the medical diagnostics field, digital information from equipment such as computer assisted tomography equipment is often presented for viewing on a laser-exposed photographic element. Such diodes generally emit electromagnetic radiation having a wavelength of from about 730 nm to about 900 nm. A common laser wavelength is about 800 nm. Other laser emission wavelengths are about 750 nm, 780 nm, 820 nm, and 870 nm. Photographic elements used in conjunction with such information-recording equipment often require filter dyes that absorb in this region, for example, as antihalation or absorber dyes.
In addition to absorbing light in the region of interest, a filter dye should leave little or no undesirable stain after the photographic element is processed, so as not to affect the image tone of the exposed and processed element. In many situations, for example in the medical diagnostics field, a cool (i.e., blue-hued) image tone is desired. Viewers often find such cool tones pleasing to the eye and conducive to the reading of stored image information. A cool tone is often imparted to photographic elements by incorporating a blue dye in the support or in a layer of the element; however, this dye usually does not perform any other useful function in the element and the cool tone imparted by this dye can be adversely effected by other retained staining dyes.
Many infrared filter dyes leave significant stain in photographic elements after processing. For example U.S. Pat. No. 4,362,800 discloses 1,1,1',1'-tetramethyl-3,3'-bis(sulfoalkyl)-1H-benz[e]indolotricarbocyanine sodium salt. This dye has been used with some success as an infrared photographic filter dye, but it tends to leave an objectionable greenish stain after processing.